1. Field
Embodiments described herein relate generally to a semiconductor storage device comprising resistance change elements.
2. Background Art
In recent years, semiconductor storage devices that use resistance change elements as memory cells have attracted attention as next-generation memories. For example, as devices that use magnetoresistive elements as memory cells, there are known a magnetoresistive random access memory (MRAM), a phase change random access memory (PRAM), and a resistive random access memory (ReRAM).
In the MRAM, a magnetoresistive element that is called a magnetic tunnel junction (MTJ) element is used as a storage element.
The MTJ element has a fixing layer where a magnetization direction is fixed by an antiferromagnetic layer, a recording layer that can freely reverse a magnetization direction, and an insulating film that is interposed between the fixing layer and the recording layer. The MTJ element uses a resistance change based on the relative magnetization direction of the recording layer with respect to the fixing layer, which is called a magnetoresistive effect.
That is, data of “1” and “0” are determined using the resistance difference based on the relative magnetization direction.
In particular, a spin injection type MRAM that uses magnetization inversion based on polarization spin current injection in a write method have attracted attention in recent years. In the spin injection type MRAM, the amount of current (inversion threshold current) that is needed to inverse magnetization is defined by the density of current flowing through the MTJ element.
A write operation of the spin injection type MRAM is executed by flowing a write current equal to or more than the inversion threshold current.
The polarity (“0” or “1”) of the data is determined according to a write current injection direction with respect to the MTJ element.